We present here a detailed study of the specific nanoparticle structures that give rise to single-molecule surface-enhanced Raman scattering (SMSERS). A variety of structures are observed, but the simplest are dimers of Ag nanocrystals. We chose one of these structures for detailed study using electrodynamics calculations and found that the electromagnetic SERS enhancement factors of 10(9) are easily obtained and are consistent with single-molecule SERS activity.

Numerous intestinal diseases are characterized by immune cell activation and compromised epithelial barrier function. We have shown that cytokine treatment of epithelial monolayers increases myosin II regulatory light chain (MLC) phosphorylation and decreases barrier function and that these are both reversed by MLC kinase (MLCK) inhibition. The aim of this study was to determine the mechanisms by which interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha regulate MLC phosphorylation and disrupt epithelial barrier function. We developed a model in which both cytokines were required for barrier dysfunction. Barrier dysfunction was also induced by TNF-alpha addition to IFN-gamma-primed, but not control, Caco-2 monolayers. TNF-alpha treatment of IFN-gamma-primed monolayers caused increases in both MLCK expression and MLC phosphorylation, suggesting that MLCK is a TNF-alpha-inducible protein. These effects of TNF-alpha were not mediated by nuclear factor-kappaB. However, at doses below those needed for nuclear factor-kappaB inhibition, sulfasalazine was able to prevent TNF-alpha-induced barrier dysfunction, MLCK up-regulation, and MLC phosphorylation. Low-dose sulfasalazine also prevented morphologically evident tight junction disruption induced by TNF-alpha. These data show that IFN-gamma can prime intestinal epithelial monolayers to respond to TNF-alpha by disrupting tight junction morphology and barrier function via MLCK up-regulation and MLC phosphorylation. These TNF-alpha-induced events can be prevented by the clinically relevant drug sulfasalazine.

Collagenase-3 (MMP13), a member of the matrix metalloproteinase (MMP) family of neutral endopeptidases, is expressed in the skeleton during embryonic development and is highly overexpressed in human carcinomas and in chondrocytes and synovial cells in rheumatoid arthritis and osteoarthritis. To determine the functional roles of Mmp13, we generated Mmp13-null mice that showed profound defects in growth plate cartilage with markedly increased hypertrophic domains as well as delay in endochondral ossification and formation and vascularization of primary ossification centers. Absence of Mmp13 resulted in significant interstitial collagen accumulation due, in part, to the lack of appropriate collagenase-mediated cleavage that normally occurs in growth plates and primary ossification centers. Cartilaginous growth plate abnormalities persisted in adult mice and phenocopied defects observed in human hereditary chondrodysplasias. Our findings demonstrate a unique role of Mmp13 in skeletal development.collagen ͉ extracellular matrix ͉ vascularization C ollagenases, a group of matrix metalloproteinases (MMPs) that act at neutral pH (1-4), have been postulated to have a role in skeletal development and bone remodeling (5-8). The MMPs are members of a large family of proteinases that have several structural features in common including the presence of a conserved zinc-binding catalytic domain (1-4). Only the products of specific MMP genes, MMP1, -2, -8, -13, and -14, however, have the capacity to cleave native, undenatured, interstitial collagens at a specific helical locus (9-13). Of the collagenases, MMP13 (collagenase-3) has been considered to have an important role in skeletal biology in view of its exclusive presence in the skeleton during embryonic development in cartilaginous growth plates and primary centers of ossification (5-8). MMP13 is also a downstream target of parathyroid hormone (PTH)-related protein (PTHrP) (14) and the transcription factor Osf2͞Cbfa1͞Runx2 in growth plate chondrocytes (15,16). In contrast to humans, where MMP1 may be strongly expressed, e.g., in inflammation, the orthologue of MMP1, McolA (12), is expressed in mice only at low levels.To examine possible functional roles of collagenases during skeletal development in vivo, we targeted a null mutation to the Mmp13 gene in mice. Our targeting strategy resulted in splicing out exon 5 that encodes the zinc-binding residues in the catalytic domain. As described here, deletion of functional Mmp13 had profound effects on skeletal development. In Mmp13 Ϫ/Ϫ embryos compared with WT embryos, the growth plates were strikingly lengthened, a defect ascribable predominantly to a delay in terminal events in the growth plates, with failure to resorb collagens, as well as a delay in ossification at the primary centers. Materials and MethodsGeneration of Mmp13 ؊/؊ Mice. We isolated two Mmp13 genomic clones from a 129͞J1 library to construct the knockout vector.The first was a BamHI͞SalI fragment that spanned from Ϸ3.4 kb of promoter sequence through the first...